I dont think it will be a complete solution, as there are other places to get kittens from, but I do believe it will help a lot, as it will limit the places people get kittens from to allow them to breed, especially in the UK compared to the US as very few pet shops sell them. Three of the local rescues will neuter kittens at 8-12 weeks old, my friends two are from one of them, and you wouldnt tell with her cats (the male is 2 now, and the female is 1), neither have had stunted growth through it, and apart from the male eating somethign he shouldn't, neither have had any health issues.
I do wish more vets would follow CP's guidelines and neuter at 4 months though, that would be a big start